EXPLORING LATE DEVONIAN MASS EXTINCTIONS AND OCEAN ANOXIA EVENTS IN UNDERSTUDIED PALEOENVIRONMENTS OF ASIA by Olivia C. Paschall Honors Thesis Appalachian State University Submitted to the Department of Geological and Environmental Sciences and The Honors College in partial fulfillment of the requirements for the degree of Bachelor of Science December, 2018 Approved by: Sarah K. Carmichael, Ph.D., Thesis Director Bob F. Swarthout, Ph.D., Second Reader Cole T. Edwards, Ph.D., Departmental Honors Director Jefford Vahlbusch, Ph.D., Dean, The Honors College 1 Contents Acknowledgements 3 Abstract 4 Preface 6 Preface Figure 8 Part I: Mongolia 9 Introduction 9 Materials and methods 12 Results 13 Discussion 14 Conclusions 16 Tables 17 Figures 21 Part II: Vietnam 26 Introduction 26 Regional geology and biostratigraphy 29 Materials and methods 31 Results and discussion 33 Geochemical analyses 33 Lithology and provenance 33 Anoxia/Redox proxies 35 Productivity proxies 38 Principle component analysis 39 Framboidal pyrite 40 Hg chemostratigraphy 41 Implications and conclusions 44 Tables 45 Figures 51 References 61 2 Acknowledgements I would like to thank Dr. Sarah Carmichael and Dr. Johnny Waters for their continued support and encouragement on this project and throughout my undergraduate education in general. They have inspired me to become a better and more confident researcher, scientist, and explorer. My success would absolutely not be possible without their patience and guidance. I can only hope to become a research scientist and educator of their caliber. Thank you to Peter Königshof, for collecting the Cat Ba samples for geochemical analysis and continued support regarding conodont biostratigraphy. Thank you to our field team in Mongolia for a productive research expedition and wonderful experience with international collaborators: Dr. Sersmaa Gonchigdorj, Dr. Ariunchimeg Yarinpil, Otgonbaatar Dorjsuren, Tumurchudor Choimbol, Ganbayar Guunchinbat, Otgonbayar Nerkhjav, Will Waters, and everyone on the Mongolian field support team. Thank you to Dr. Bob Swarthout for being the second reader of my thesis and for providing insightful feedback. I would like to thank my research partner-in-crime Allison Dombrowski for encouragement and companionship in Mongolia as well as during late nights in Rankin. Thank you to my sources of funding, including Appalachian State University, Southeastern Section of the Geological Society of America, American Association of Petroleum Geologists, and the Explorers Club. Thank you to Anthony Love for patient guidance on preparing samples for SEM analysis. Thank you to my wonderful support system, including but not limited to: my parents, Devin Hoffman, Kevin Bynum, Delaney Ryan, and Victoria Haynes. 3 Abstract The Devonian-Carboniferous (D-C) transition (359 Ma) was a period of rapid global faunal changes in conjunction with global cooling and widespread ocean anoxia. The end- Devonian mass extinction is one of the top 10 mass extinctions in Earth’s history, and the associated anoxia and regression is referred to as the Hangenberg Crisis. In many locations, the Hangenberg Crisis is characterized in the rock record by sandstone and black shale deposits. Little is known about the Hangenberg Crisis in Southeast Asia, however. Here we show that the Hangenberg Crisis is recorded within the Pho Han Formation on Cat Ba Island in northeastern Vietnam, and at the Hoshoot Shiveetiin Gol locality in the Hovd Province of southwest Mongolia. Preliminary work in July-August 2018 at the Hoshoot Shiveetiin Gol locality in Mongolia reveals that the Late Devonian shallow marine sequence is relatively continuous and encompasses the entire Late Devonian timescale, including both the Frasnian- Famennian and Devonian-Carboniferous transitions. Although no black shale is present at the locality due to the location’s paleotopography, we interpret a pronounced arkosic sandstone layer to represent the Hangenberg regression event. In contrast, the Cat Ba Island section in Vietnam represents a sediment-starved basinal facies on the South China carbonate platform, where long-term dysoxic/anoxic conditions (as determined by trace element proxies, increased total organic carbon, and framboidal pyrite distributions) persisted. More severe anoxia (approaching euxinia) exists within the Hangenberg Crisis stratigraphic interval. Mercury (Hg) chemostratigraphy reveals a significant enrichment that corresponds to the Hangenberg Crisis and the D-C transition. The Hg is most likely sourced from volcanic emissions, potentially linking the end-Devonian anoxia and mass extinction to large-scale volcanic activity. This is a new and valuable 4 development that is supported by very recent studies in Uzbekistan and Germany and must be investigated further. As both sites represent the two end members of understudied paleoenvironments (compared to sites in Europe and North America, where overlapping signals can be difficult to interpret), they are critical to understanding Late Devonian anoxia and extinction events. 5 Preface This thesis is a product of the research I have completed over the past three years with the DAGGER (Devonian Anoxia, Geochemistry, Geochronology, and Extinction Research) research group. We are an international and interdisciplinary research team affiliated with the UNESCO International Geoscience Programme’s (IGCP) Projects 580, 596, and 652. Our team primarily studies two stages of Late Devonian ocean anoxia and mass extinction events: the Frasnian-Famennian extinction (372 Ma) which corresponds to the Kellwasser anoxia event, and the Devonian-Carboniferous extinction (359 Ma) which corresponds to the Hangenberg anoxia event/crisis. These extinction events are collectively called the Late Devonian mass extinction, which is one of the “big five” mass extinctions in Earth history (Raup and Sepkoski, 1982; McGhee, 2013), but it is arguably the least understood of them. Unlike the other massive extinction events, no single trigger is apparent, and our understanding of Late Devonian anoxia events is limited by concentrated study locations in North America and Europe (which were geographically adjacent during the Devonian as Pangaea was forming). The depositional histories at these sites that were situated on the Euramerican continent are complicated by the building and shedding of the Appalachian Mountains during the Variscan/Appalachian orogeny. For this reason, the DAGGER team studies unique and underrepresented paleogeographic locations that are independent of this orogenic event. My thesis incorporates research from two locations in Asia, where relatively little is known about the Late Devonian anoxia and extinction events (Fig. P-1). These two locations represent endmembers in terms of depositional settings: the first being an open ocean island arc complex, and the second representing a restricted basin not being affected by mountain building/shedding that often overprints true ocean anoxia signatures. The lithologies that define the Hangenberg Crisis in these locations are 6 very different when compared to the type section in Germany, which preserves a very specific and unusual paleoenvironment. Part I of my thesis is based on 2018 fieldwork in the Khovd Province of Mongolia. Previous fieldwork in 2012 and 2014 was completed by DAGGER members. The field site of particular interest to this study is called Hoshoot Giveetiin Gol, which contains Late Devonian stratigraphy that records the events associated with both the Frasnian-Famennian and Devonian-Carboniferous boundaries. My job in the field was to make a geologic map of the site in order to assess the usefulness of radiometric dating of a basalt flow, as well as to determine if the section is stratigraphically continuous in the area of interest. This will serve as a jumping off point for studies by future DAGGER members, who will use multi-proxy geochemical and lithological analyses, similar to those used in Part II of this thesis. Part II of this thesis focuses on a stratigraphic section at Cat Co Beach on Cat Ba Island in northeastern Vietnam. This section includes and expands upon my first-author manuscript that has been submitted to the journal Global and Planetary Change. The manuscript is entitled “The Devonian-Carboniferous boundary in Vietnam: sustained ocean anoxia with a volcanic trigger for the Hangenberg Crisis?” The purpose of this study was to investigate how the Hangenberg Crisis is recorded in a historically anoxic basin, both geochemically and lithologically. The lithologic section was described and analyzed for conodont biostratigraphy in Komatsu et al. (2014), and my study is a geochemical and mineralogical continuation of this work. I used geochemical, principle component, and framboidal pyrite analyses to locate and interpret the severity of the Hangenberg Crisis within the section. Investigating mercury chemostratigraphy allowed me to propose widespread volcanism as a potential trigger of the Hangenberg Crisis. 7 Preface Figure Figure P-1. Paleogeographic reconstruction of the continents during the Late Devonian with thesis study locations in red. Most Late Devonian study locations were within Euramerica during the Devonian. Figure modified from Blakey (2016), using updated paleogeographic data for Asia from Xiao et al. (2010) and Metcalfe (2009). 8 Part I MAPPING LATE DEVONIAN MASS EXTINCTIONS AND ANOXIA EVENTS AT THE HOSHOOT SHIVEETIIN GOL LOCALITY IN THE KHOVD PROVINCE OF MONGOLIA 1. Introduction The discovery of anoxia indicators in the West